Agilent Technologies 856290216 service manual Al6 Assembly Fast ADC Circuits Option

Al6 Assembly Fast ADC Circuits (Option 007)

The fast ADC consists of video signal scaling and limiting amplifiers, an 8-bit flash ADC, peak/pit detection of the digitized video signal, a 32 K-byte RAM, and the fast ADC control circuitry.

Video Input Scaling Amplifiers and Limiter

Refer to function block L of the Al6 fast ADC assembly schematic diagram in the

HP 8560 E-Series Spectrum Analyzer Component Level Information.

The video input scaling amplifiers help provide scaling (10 dB/div, 5 dB/div, 2 dB/div, or

1 dB/div) and buffer the flash video output. When the GAINX2 control line is low, switch U44D is open and switch U44C is closed. Thus, the scaled video at TP26 virtually follows the video input (0 - 1 V). When the GAINX2 control line is high, switch U44C is open and switch U44D is closed. Amplifier U43 then provides a gain of 2(Vi,) -1 V. Voltage clamp CR4 prevents the scaled video input to amplifier U45 from going more negative than -0.35 V or more positive than t1.25 V.

Note	When measuring voltages or waveforms on the Al6 fast ADC assembly,
	connect the ground (or common) lead to the ground-plane trace on the Al6
	assembly. This digital ground plane is totally isolated from the chassis.

1. Press (PRESET) on the Option 007 spectrum analyzer and set the controls as follows:

Centerfrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz Reference level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -10 dBm Log/division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dB/DIV Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 ms

2.Connect the CAL OUTPUT to the INPUT 500 connector.

3.Adjust the Option 007 spectrum analyzer reference level to place the signal at the top graticule line on the CRT display.

4.Measure the dc level at TP25. If the voltage measured is not +l.O f0.15 V, troubleshoot the A3 interface assembly.

5.Measure the dc level at TP26. The level should be approximately the same as the level measured at TP25. If not, suspect switch U44.

6.Set the Option 007 spectrum analyzer scale to 5dB per division.

7.Adjust the Option 007 spectrum analyzer reference level to place the signal at the top graticule line on the CRT display.

8.Measure the dc level at TP25 and TP26. The level should be i-1.0 f0.25 V. If the level measured at TP26 differs from the level measured at TP25 by more than 0.25 volts, troubleshoot U43 and associated circuitry.

9.Disconnect the CAL OUTPUT signal from the INPUT 500 connector.

10.The level at TP26 should drop to -0.35 Vdc. If the level is less (more negative) than -0.35 Vdc, replace voltage clamp CR4.

ADC/lnterface Section 8-31